As far as Checkpoint America, I don't believe Dan Gurney had any involvement. ...Back in 1974, when I spoke with them, it was owned by Bob (Vanderhoof) or (Vanderhoot). [CRS strikes again!]
The Checkpoint America conversion was not sold as a kit. ...Turbo installations had to be done by them. ...That is why I designed my own.
Checkpoint America used a Rajay turbo, which did have a seal on the suction side. ...Air Research also had a small turbo which used a seal on the suction side. ...At that time, it was very difficult to purchase a single turbo, as those companies wanted to deal on a larger scale.
Crane Cams (in Hollandale, Florida) was just getting into the turbo business and selling components. ...They were in process of developing kits, but that never progressed. ...I became a Crane distributor (long story) and was able to buy direct from them. ...They used Schwitzer turbos, which had a "piston-ring" type seal on the suction side, and were not good if subjected to high manifold vacuum.
The Schwitzer turbo was fine for a blow-thru (the carb) system, but weighing the pros & cons, I wanted a draw-thru system ...I incorporated a design to isolate the compressor side of the turbo from manifold vacuum, yet it could still "free-wheel" to reduce turbo lag.
Back then there was little information about turbocharging available. ...Many people that knew wouldn't talk, and many people that talked, didn't know! ...I learned a lot through trial & error.